Treatment Outcomes of Postoperative Ultra-Hypofractionated Stereotactic Body Radiotherapy in Prostate Cancer

Abstract

<h3>Purpose/Objective(s)</h3> Prospective randomized phase 3 trials have shown that hypofractionated radiotherapy (RT) regimens are safe and effective for definitive prostate RT. There is, however, a scarcity of data describing the outcomes of ultra-hypofractionation in the postoperative setting. The purpose of this study was to assess the safety of ultra-hypofractionated RT to prostate bed using stereotactic body RT (SBRT) technique. <h3>Materials/Methods</h3> The clinical data of 69 prostate cancer patients who received postoperative prostate bed SBRT between August 2018 and September 2020 were reviewed retrospectively. All patients had had radical prostatectomy, and 44 (63.8%) had pelvic lymph node dissection, with a median of 14 (range: 2–34) lymph nodes dissected. The primary endpoints were failure from biochemical failure (FFBF) and acute and late gastrointestinal (GI) and genitourinary (GU) toxicities. Secondary endpoint was progression free survival (PFS). <h3>Results</h3> The median age was 64 years (range: 43–76 years). Thirty patients (43.5%) received adjuvant RT and 39 (56.5%) had salvage RT median 12.4 months (range: 1.5–137.6 months) after surgery. Median SBRT fraction and total doses were 7 Gy (range: 6–7.3 Gy) and 30 Gy (30–36.5 Gy), respectively delivered in 5 days. Majority of patients (82.7%) had high risk disease and only 13 patients (18.8%) had lymph node metastasis. Seminal vesicle invasion was observed in 22 patients (31.9%) and 49 patients (71%) had extracapsular invasion. Forty-eight patients (69.6%) had positive surgical margin. Pre-SBRT and post-SBRT PSA values were 0.37 ng/mL and 0.05 ng/mL, respectively. 27 patients (39.1%) also received adjuvant androgen deprivation therapy (ADT) after SBRT and post-treatment PSA nadir value was 0.01 ng/mL. Median follow-up time was 23.8 months (range: 2.8–37.2 months). The 2-year FFBF and PFS were 91.4% and 87%, respectively. Seven patients (10.1%) had BF median 18.5 months (range: 1.7–33.5 months) after completion of SBRT. Disease progression was observed in 10 patients (14.5%) median 13.9 months after treatment. Acute GI and GU system toxicities of grade 2 or greater were observed in 13% and 14.5% of patients, respectively. Late GI and GU toxicities of grade 2 or greater were observed in 4.3% and 16% of patients, respectively. <h3>Conclusion</h3> SBRT delivered to the prostate bed over a 5-day period was found to be safe, with acceptable acute and late toxicities. Longer follow-up and randomized trials with a large patient population, however, are required to validate our findings.